SM Seismology
Can we predict earthquakes?

Can we predict earthquakes?

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The Seismology and Natural Hazards Divisions of the European
Geosciences Union (EGU) heard seismology experts to summarise the
current status of earthquake prediction.

Earthquakes, such as the 2011 Tohoku , the 2011 Christchurch and the
2010 Maule earthquakes, or the 1999 Afghanistan and 1999 Turkey
earthquakes, are often devastating, resulting in wide-spread
infrastructural damage and high number of fatalities. But even
moderate-size events, like the April 06, 2009, L’Aquila earthquake (Mw
6.3), may create local disasters and tragic losses of properties and
human lives. The public and decision makers are, therefore, interested
in information about the time and location of future events. However,
despite considerable research effort, scientists are only capable of
making estimates about where big quakes are most likely to happen in the
long term (years to decades). There is yet no reliable way of
predicting in the short term (days to weeks or months) when an
earthquake of a given size will occur in a specific location.

Why are earthquakes hard to predict?

Earthquake generation is a very complex process deep in the Earth
crust. The magnitude and timing of a large quake depends on various
factors such as the size of a fault section and the amount of stress
accumulated there. Measuring the stress is an engineering feat in
itself, as it requires drilling into the ground for several kilometres.
Furthermore, scientists do not know precisely how much stress it takes
to break a fault. However, once enough stress has accumulated, even a
low-magnitude earthquake may cascade into or trigger a large tremor.

A possible strategy to predict earthquakes would consist in finding a
diagnostic precursor. This precursor should be an observable signal,
such as a deformation of the ground, anomalous emission of radon gas
from the Earth’s interior, or strange animal behaviour, detected before
any tremors. This diagnostic signal then indicates – with high
probability and strong statistical significance – where, when, and with
what magnitude an earthquake will occur. However, this “silver-bullet”
strategy of earthquake prediction has not yet provided a successful and
statistically stable prediction scheme. The International Commission on
Earthquake Forecasting for Civil Protection analysed a series of
proposed precursors in 2011 and concluded that none of them offers a
reliable diagnostic of an impending earthquake.

Operational earthquake forecasting

As an alternative to earthquake prediction, scientists focus on
developing earthquake forecasts, that is, on quantifying the likelihood
of an event occurring. Researchers determine these probabilities of
occurrence to inform communities about seismic hazards who, in turn, can
use the data to make decisions before an earthquake.

Earthquakes tend to occur closely spaced in time at a given location,
as so called earthquake clusters or earthquake sequences (the
aftershocks that follow the mainshock are an example). “Events that have
happened in a region are analysed for clustering, and from this
knowledge seismologists are able to construct a probability model for
future events,” explained Charlotte Krawczyk, president of the EGU
Seismology Division. These probability models then allow researchers to
forecast the likelihood of future tremors occurring at a given location.

Using short-term models, scientists can determine if there is an
added probability of an earthquake happening at a given location in a
period of a few days to a week. Modelling can show that the likelihood
of an event occurring in that period and location increased “from 1 in
10,000 or 1 in 100,000 to 1 in 100 or 1 in 1000,” according to Paolo
Gasparini, professor of geophysics at the University of Naples. But the
absolute probability of an earthquake happening remains low, “lower than
1%,” he adds.

Warner Marzocchi, chief scientist of Italy’s National Institute of
Geophysics and Volcanology defended that it is up to decision makers to
use these probabilities to take mitigation actions. He stressed,
however, that “the mitigation actions should be light, in the sense that
most of the times warnings turn out to be false alarms, and therefore
decision makers have to be careful to minimise complains and lose
credibility.” He added: “Each individual might be inclined to do what is
in his or her best safety interest, being given an informative hazard
advisory by authorities.”

Davide Miozzo expert in communication of risk prediction from the
CIMA Research Foundation in Italy, warned about the cry-wolf syndrome:
“If communication is excessively recurrent and redundant it will be
disregarded. And once institutions lose the population’s trust, the
population itself becomes more vulnerable and less resilient to natural
adversities.”

Experts agree that the most effective way of reducing risk and
preventing damage is to use operational earthquake forecasting to build
long-term probability models for future events. These are then used to
inform earthquake engineers on seismic hazard that can be used to devise
proper seismic safety designs. “Long-term forecasting models are the
base of hazard maps used for civil protection, establishing building
codes and for retrofitting regulations,” said Prof Krawczyk.

“Most important,” Dr Marzocchi concluded, “every kind of mitigation
actions in the short-term will not replace the best long-term action
that is to build buildings that can resist earthquakes.”

About EGU

EGU, the European Geosciences Union, is Europe’s premier geosciences union, dedicated to the pursuit of excellence in the Earth, planetary, and space sciences for the benefit of humanity, worldwide. It was established in September 2002 as a merger of the European Geophysical Society (EGS) and the European Union of Geosciences (EUG), and has headquarters in Munich, Germany.